Mouthpiece.



E. D. SPEAR.

MOUTHPIECE. APPLICATION FILED JAN. 26. 1915.

Patented June 27, 1916.

Tm: COL mum PLANOGRAPH c0., WASHINGTON, n. C.

EDMUND I). SPEAK, 015 BOSTON, MASSACHUSETTS.

MOUTI-IPIECE.

Specification of Letters Patent.

Patented June 27, 1916.

Application filed January 26, 1915. Serial No. 41,550.

To all to 700m it may concern I Be it known that I, EDMUND D. SreAn, of Boston, in the county of Suffolk and l tate of Massachusetts, have invented a new and useful Improvement in Mouthpieces, of which the following is a specification.

My improvement is designed primarily as an embouchure or mouthpiece to amplify or increase the intensity of the tones of the human voice when presented to the transmitter of a telephone, but more especially to permit the speaker to segregate orcondcnse such tones in a way'or manner to prevent their actuating other and outside masses and contiguous columns of air likely to convey the sound waves to other persons ears or other telephone transmitters or to sound collectors in proximity to or in the vicinity thereof. Notably this device prevents listening persons other than the one making use of a telephone to hear conversation carried on through it in the usual way. Except in those unusual instances when the diaphragm of the receiver is forcibly vihrated in talking this device makes communications practically secret and noiseless.

As the result of investigations which I. have made and in view of the character of transmitters now in general use, their size and location, I have constructed a device containing a chamber of such a shape as will correspond exactly with the actual form of wave movements and so far as possible with the theoretical shape of the sound waves. My observations showed that these waves or movements occurred along lines of least resistance which were found to be conchoidal, and as a result my invention consists of an eggshaped structure the interior of which provides an ovoid chamber (literally egglike and therefore conchoidlike, since eggs are conchoidally curved) open at one end to fit over the ordinary mouthpiece of a telephone transmitter and at the opposite end to receive the speakers lips. The ovoid form of this chamber must be retained without any extensive break in continuity of its curved inner surface from one end to the other, that is, there must be no substantial interruption or obstacle to the general forward movement of the sound waves. In other words, they must not be obstructed although they may be led spirally. I have found also the necessity of providing reversed curves from the outer to the inner end of the chamber as the result of a. study of the phenomena of interference or screen effects in acoustics.

hen conchoidally curvedsound waves act upon masses or columns of air confined within the sides of cylindrical tubes or in megaphones having straight walls with constantly expanding or cone-shaped forms, it may be assumed that the motion of the air columns in either instance occurs in a rotating and spirally twisting way.

In the case of the cylindrical tube, for example (unless extremely short and therefore acted upon only by tones of very short wave length) reflection from one side to another of the sound movement takes place and because this movement is irregular While the shape of the contained air in the tube is regular, the attempt to break up or destroy this regularity by the passage of sound waves results in interference.

WVith the use of a. device having an ovoid chamber interference is prevented and every opportunity is provided for securing the best results in the telephone transmitter with the least effort.

In other words, with my mouthpiece very little energy need be expended to secure aresult which would otherwise require quite loud talking, and consequently one may speak wlth such a low tone as not to make himself audible to one nearby and yet make himself easily understood at the telephone receiver.

A proper conchoidal shape also makes unnecessary any damping or silencing attachment or material such as is sometimes used acoustically, although in those instances when the line is open and this device is adjusted to the transmitter it was noticed that certain loud sounds were picked up by the mouthpiece as by a resonator. The addition of a covering cap although not necessary may be used to take the place of ones hand often so used to cut out objectionable sounds or to prevent the transmission of conversation in the transmitting room while the telephone is in circuit but not in use.

My invention will be understood by reference to the drawings in which it is shown in use in its preferred form.

Figure 1 is an elevation of my improved device in place on the mouthpiece of a telephone. Fig. 2 is a similar view, my device being shown in section.

A is the transmitter 01 an ordinary telephone.

B is my mouthpiece which may be spun or otherwise constructed of sheet metal or other material. Its end I) is open and of suiiicient size to fit over the ordinary telephone mouthpiece a and rest against the plate a which surrounds the base of the mouthpiece a. The other end of the device is open as at i') and into it the user talks, holding the device in place by hand. Between the ends the receptacle swells out as at b and then recedes as at b and connects with the end I), the entire curve being approximately that known as the coiichoidal curve, a curve which may he mathematically calculated. The interior grooves or beads 12' and 7) are not essential, being the result only of a simple process of construction and of such size as not to interfere with the progress of the sound waves in passing through the resonance chamber 1) formed in the receptacle.

The device may be permanently attached to the telephone but preferably it is separate therefrom. When it is to be used it is slipped over the mouthpiece and held in place by hand. In talking the mouth is placed close to the opening and because the sound waves from the mouth of the talker are directed toward the telephone diaphragm and meet with no interference in their progress, they may be of compara- Oqlu of this potent may be obtained for lvo cents tively little strength and yet be of sufiicicnt force to establish vibrations of the telephone diaphragm. Thus one can speak into the mouthpiece so softly that ones voice will not be heard in a room and yet will transmit an intelligible message over the telephone system.

The interior walls of the chamber should for the best results be exactly ooiiclioidal though a slight variation may be made from the mathematical conchoid without departing from the theory underlying my invention, which contemplates an oven! chamber.

hat I claim as my invention is 1. A device of the kind described comprising a ieceptacle having an opening at each end and containing a chamber connecting said opei'iiiigs, the interior walls of which are coiichoidal, one end of said device being adapted to fit over the mouthpiece of a telephone and the other end to receive the mouth.

2. A device of the kind described comprising a receptacle having a chamber withiii it, one of the ends of said chamber being connectible with a telephone mouthpiece and the other end being adapted to be used as a mouthpiece, the interior walls of said chamber being curved conchoidally to a]- low the passage of sound Waves therethrough Without interference.

EDMUND D. SPEAR.

\Vitnesses:

J ALLEN CROSBY,

ARTHUR SCHNEIDER.

each, by addressing the "Commissioner of Patents,

wumm, D. O." 

